MKI67, alternately referred to as Ki-67 and Ki-67 antigen, is an endogenous marker for cellular proliferation and a traditional marker of neurogenesis. MKI67 is present in the nuclei of dividing cells during the G1, S, and G2 phases of mitosis, however it is not found in significant amounts in resting or G0 phases. Because MKI67 protein is found in most proliferating cells, including tumor cells, it has become well-established marker for the growth function of a given cell. For instance, the fraction of Ki-67-positive tumor cells is often correlated with the clinical progression of different cancers, such as prostate or breast cancers. The ‘growth factor’ or ‘Ki-67 index’ of a population of cells, for instance tumor cells, may be utilized for various purposes, for instance for prognostication of tumor development, or for determination of appropriate therapeutic strategies for a given proliferative disease such as cancer (Scholzen and Gerdes 2000).
MKI67 has been used in various studies as a marker for neurogenesis in the brain. For instance, MKI67 was measured alongside doublecortin (DCX), a marker for early or new neural progenitor cells, to study hippocampal neurogenesis and neuronal migration in various mouse strains (Kim et al., 2008). In another study, MKI67 was again measured alongside DCX to investigate the potential decline in neurogenesis in adult dogs (Pekcec et al. 2008). These studies highlight the utility of MKI67 in the study of neurogenesis.
Minimal human promoter elements which are capable of driving expression in specific cell types and/or in specific regions of the brain are of interest. Also of interest is the identification of minimal elements required for adequate expression and specificity that allow ease of use in expression constructs.